Mail processing systems for preparing mail pieces, e.g., stuffing envelopes, and/or printing postage indicia on envelopes and other forms of mail pieces have long been well known and have enjoyed considerable commercial success. There are many different types of mail processing systems, ranging from relatively small units that handle only one mail piece at a time, to large, multi-functional units that can process thousands of mail pieces per hour in a continuous stream operation. The larger mailing machines often include different modules that automate the processes of producing mail pieces, each of which performs a different task on the mail piece. Such modules could include, for example, a singulating module, i.e., separating a stack of mail pieces such that the mail pieces are conveyed one at a time along the transport path, a moistening/sealing module, i.e., wetting and closing the glued flap of an envelope, a weighing module, and a metering module, i.e., applying evidence of postage to the mail piece. The exact configuration of the mailing machine is, of course, particular to the needs of the user.
Typically, a control device, such as, for example, a microprocessor, performs user interface and controller functions for the mail processing system. Specifically, the control device provides all user interfaces, executes control of the mail processing system and print operations, calculates postage for debit based upon rate tables, provides the conduit for the Postal Security Device (PSD) to transfer postage indicia to the printer, operates with peripherals for accounting, printing and weighing, and conducts communications with a data center for postage funds refill, software download, rates download, and market-oriented data capture. The control device, in conjunction with an embedded PSD, constitutes the system meter that satisfies U.S. information-based indicia postage meter requirements and other international postal regulations regarding closed system meters.
In order for these automated mailing machines to be effective, they must process and handle “mixed mail.” The term “mixed mail” is used herein to mean sets of intermixed mail pieces of varying size (for example, from postcards to 9″×12″ flats), thickness (for example, from 0.007 inches thick up to 0.75 inches thick), and weight (for example, from less than one ounce up to several pounds). In addition, the term “mixed mail” also includes stepped mail (i.e., an envelope containing an insert which is smaller than the envelope to create a step in the envelope), tabbed and untabbed mail products, and mail pieces made from different substrates. Thus, the range of types and sizes of mail pieces which must be processed is extremely broad. In known mixed mail handling machines which separate and transport individual pieces of mail away from a stack of mixed mail, the stack of mixed mail is first loaded onto some type of transport system for subsequent sorting into individual pieces of mail. The mail piece is conveyed downstream utilizing the transport system, such as rollers or a belt, to each of the different modules (as described above) for processing.
One such module can be a weighing module to calculate the weight of a particular mail piece, or determine that some predetermined threshold is not exceeded, as it is being processed. The calculated weight (or threshold) is provided to the control device for calculation of the postage amount required for the mail piece based on the actual weight. In some weighing modules, the mail piece is temporarily stopped on the scale of the weighing module while the weight is measured, while in others the mail piece is not completely stopped and a weight measurement is made while the mail piece is in motion. In either case, it is necessary to ensure that an accurate weight has been determined, or accurately determine that the mail piece does not exceed a threshold amount, since the postage amount is determined based on the actual weight or threshold amount. If the weighing module does not accurately weigh a mail piece or determine that it is below the threshold amount, the amount of postage applied to the mail piece will either be too little, resulting in possible non-delivery of the mail piece, or too much, resulting in a loss of funds. The need for accuracy in determining the weight to be used for calculating postage provides constraints on the time required to determine the weight. In automated mailing machines, there is a constant need to increase the rate at which the scale can determine the weight (or that the mail piece does not exceed a threshold weight) of a mail piece such that the overall throughput of the machine can be increased. A basic cause of the delay in determining weight for a mail piece is the tendency of the scale to oscillate when a mail piece is being transported (or stopped) on the scale. These oscillations are damped as the scale settles, but only slowly will the scale arrive at a stable output value representative of the weight of the mail piece. To determine the weight of a mail piece, or that the weight of a mail piece does not exceed a predetermined threshold weight, as quickly and accurately as possible, it is desirable to minimize the external forces on the scale that can cause the scale to oscillate, thereby reducing the time required to determine a weight.